BANGKOK, Thailand -- A U.S. Pacific Command (PACOM) search and rescue team and Thai Navy SEALs were unable on June 28 to find 12 Thai boys and their soccer coach in a dark, monsoon-flooded cave in northern Thailand after they disappeared in its six-mile (10-kilometer) maze of stalactites more than five days ago.

A British rescue team also joined in the search, supporting nearly 1,000 Thai military and civilian personnel, but incessant rain has flooded the cave so deeply that scuba divers found it difficult to swim through narrow, jagged passageways.

The tragedy at the cave has become a national fixation with non-stop television coverage on the plight of the 13 missing people, the rising flood waters inside the cave, the inability of scuba divers to wedge themselves through twisted rock formations, and other hazards.

Helicopters, hand-launched drones, and people on foot explored jungle-clad mountains above the cave to find other possible entrances or holes in the ground leading into its chambers.

The U.S. team included Special Forces Airborne troops and others, according to their camouflage uniforms' patches.

"The United States Pacific Command (PACOM) has sent a search and rescue team at the request of the Royal Thai government to assist in locating the group," the U.S. Embassy in Bangkok said on June 28.

"As the team accesses the environment and develops potential courses of action, all options for rescue operations are being considered in close coordination with Thai rescue personnel," the embassy said.

It was unclear how deep the PACOM team were able to go into the cave on June 28 because rain reportedly forced Thai officials to scale back some operations.

"They have come with set of underwater equipment with sonar system, which also can dive down underwater," Chiang Rai Governor Narongsak Osatanakorn told CNN.

The team included rescue paratroopers, a survival specialist and support personnel, U.S. Air Force public affairs officer Jessica Tait told CNN.

The Thai military meanwhile dragged an industrial drill up the mountain and began drilling on June 28 where geologists hoped to puncture the cave's ceiling and drop supplies and search teams.

On June 23, more than five days ago, the 12 boys and their 25-year-old coach walked into the cave after abandoning their bicycles at the entrance and, at about 2 miles (3 kilometers) deep, shed their sandals and backpacks.

Barefoot, carrying only snack food and trapped with little oxygen in the cave's darkness, they left behind footprints in the muddy floor and a few wet handprints along the rocky walls.

The 13 people were apparently unable to leave the cave after rising water blocked their escape, so they trudged deeper into its unexplored interior while, behind them, additional chambers also flooded.

Thailand's military government inserted electric cables, lighting, air ventilation systems, water drainage pumps and telephone communication equipment into the cave which meanders under rugged, isolated, jungle-clad mountains in northern Thailand near Chiang Rai along the border with Myanmar.

On June 28 the rain was so heavy that some portable electric generators powering the drainage and other systems had to be temporarily shut amid fears of a short-circuit causing an electric fire or exploding, officials said.

Tham Luang Cave in Nam Nang Non Forest Park is a tourist attraction except during the annual June to October monsoon season which has been dumping unusually heavy rain on the area.

That rain was soaking through the cave's lengthy ceiling and repeatedly filling up inner chambers.

It was unclear why the boys, aged 11 to 16, and their coach decided to explore the cave during a June 23 break in their nearby practice games in Mae Sai district.

When they failed to emerge on June 23 evening, distraught parents contacted officials who launched a search, but they were unable to probe deeply because of the flooded passages.

Makeshift attempts followed until the Thai Navy Special Warfare Command flew in a SEAL team of 17 men trained in demolition and underwater maneuvers on June 25.

They plunged into murky water shallow enough to wade through in some places, but in other sections required their scuba gear.

"One of the problems the divers have faced is that the water is very muddy, which has impaired visibility," First Special Forces Regiment Chief, Capt. Anan Surawan told reporters.

Unable to see despite using underwater lights, the SEALs had to occasionally surface to get their bearings.

But when rain caused chambers to fill up to the ceiling, they were unable to surface and could not proceed, officials said.

If found alive, the boys may have to quickly learn basic scuba diving techniques to enable them to escape with the SEALs, officials said.

Relatives and villagers meanwhile performed Buddhist and animist rituals at the cave's muddy entrance, banging drums and gongs, burning incense and candles, praying, and offering food to the cave's "spirits" while begging them to "release" the 13 missing people.

Some men waved large, circular fishing nets inside the cave's entrance to catch "lost spirits" and remove them from hampering the search.

Geologists studied hand-drawn maps of the cave which begins at the tourist-friendly entrance where cement and metal stairs, hand rails, and large photogenic chambers offer an exciting experience.

That passageway deteriorates into a forbidding labyrinth of stalactites, mud and water into which tourists would usually not venture, and forks after 2 miles (3 kilometers).

One route veers north a few more miles (kilometers) to an apparent dead-end.

The other longer branch runs south on a 4-mile (7-kilometer) route where SEALs suspect the missing group may have gone.

SEALs found the boys' sandals and backpacks where the cave forks just before a 50-foot (15-meter) deep flooded area at the beginning of the southern route.

Rescuers hoped the group was still alive near the very end of the southern route, along its unexplored cul-de-sacs.

Helicopters and small drones meanwhile hovered over vertical holes in the jungle hoping a natural-formed "chimney" would lead through to the cave's ceiling on that southern route.

After heavy rain forced the helicopters to temporarily stop flying on June 28, rescuers tried to reach the steep zones on foot.

They dropped emergency food and other supplies into one hole along with a note advising the group to stay at that spot if possible and await rescuers.

The industrial drill was brought in to widen narrow holes so rescuers could rappel down.

"We are still optimistic they are all alive," Defense Minister Prawit Wongsuwon told reporters on June 25.

"Even though they may not have anything to eat, they should have water to drink," retired Army Gen. Prawit said.

Reducing the high water was a main priority, and the army was bringing in more motorized siphons.

Large ventilation hoses meanwhile pumped fresh oxygen so rescuers, and hopefully the 13 missing people, could breathe.

The cave's thick rocks block smartphone and walkie-talkie signals, so telephone land-lines and electric cables were laid to permit communication with rescuers and officials at the cave's entrance.